In an analog video communication, such as in the analog broadcasting communication, video information in a new channel can be seen immediately when the current channel is changed into the new channel. However, in a digital video communication, video contents are usually transmitted in a coded way so as to save the network bandwidth. In such scheme the video contents at the source side are encoded into a series of packets before being transmitted over the network; at the destination side, the receiver receives and decodes the video packets for playing out. In addition, in order to protect packet losses, channel coding scheme such as Forward Error Correction (FEC) is usually used. Both video source coding and channel coding require a block of data to be processed at a time, therefore, a delay corresponding to at least one block of data is required when a channel change is requested. Thus, there is a period of time during which video blanking occurs until the information from the new channel occurs. This invention addresses the delay caused by channel coding especially FEC and proposes solution to reduce the delay and therefore the blanking time period at a channel change.
A good FEC encoding needs a large block size of the video information, and the FEC efficiency depends on the block size of FEC encoding. A bigger block size can have better error correction performance with less redundancy. However, big block size means more initial delay for the video stream of the new channel because a delay corresponding to at least one block size of video is required to get the first frame of video. If the TV programs' initial delay at the startup and/or the channel change will be too long, and will make the audiences feel uncomfortable. Usually, the customer can tolerate only 2-3 seconds channel change time. While an efficient channel coding may require 10 seconds even more initial delay (buffering).
A method and a video signal processor in the prior art is provided to reduce blanking time between changing from one program channel to another program channel. In the method, the video information of the current channel is buffered at a memory, and replaces the video blanking by continuing to broadcast the buffered video information during the channel changing. However, this method does not reduce the channel changing time actually. In addition, since the video information from the old channel can be seen after the command of changing channel has been transmitted, the user will be confused and does not know whether the command has effected.
Another method in the prior art is provided to eliminate the video blanking during the channel changing. In the method, various information such as text information, advertising or electronic service guide information is provided to replace the video blanking. However, similar to the above method, this method still does not reduce the channel changing time, and the user may think those information are unnecessary.
Therefore, it is needed to provide a method to overcome the above disadvantage in the prior art, so as to not only reduce the program startup and/or channel change time but also assure the channel changing efficiency.